Generally, as a screen becomes wider, a viewer's angle of view can be implemented a various ways. Furthermore, the viewer can focus on an entire image, and can concentrate on the screen with a high sense of realism. Accordingly, demands for a large display device continuously increases. As techniques for manufacturing a large display device are developed, large and flat type display devices are being rapidly presented onto the market.
In order to have an optimal concentration degree at a wider viewing angle in a TV receiver, a viewer has to move closer to the television screen. However, due to the recognition characteristics of human eyes, it is not preferable for the viewer to come too close to the screen. That is, when the viewer approaches to the television too closely, each pixel inside an image may be individually perceived. This may cause the viewer to feel uncomfortable when viewing images and thus result in fatigue.
The reasons for this may be explained in reference to a contrast sensitivity function with respect to a spatial frequency. For instance, as shown in FIG. 1, experiments were conducted to determine whether human eyes could recognize stripes in a state that a density of the stripes was varied within a viewing angle of 1°. According to the experimental results, it has been reported that the human eyes have certain characteristics as shown in the graph of FIG. 2 (Contrast Sensitivity of the Human Eye and its Effects on Image Quality, Peter G. J. Barten, SPIE Press Monograph Vol. PM72, 1999). More concretely, when about 8 stripes are repeatedly implemented within a viewing angle of 1°, the human eyes can best recognize the patterns. However, when the number of the stripes increases, a recognition degree by the human eyes is decreased. If the number of the stripes increases to about 60, the human eyes cannot recognize the stripes as being black lines, but can only recognize such stripes as being gray lines. According to the experimental results, when the spatial frequency is more than 60 cpd (cycles per degree), the human eyes cannot recognize an image clearly, but can only recognize the image as a soft or blurred image. Therefore, in order to allow the viewer to comfortably view an image with minimal fatigue, the spatial frequency should be set as 60 cpd.
Also, the viewer should watch television within an optimal viewing range where a viewing angle can be increased and an image can be recognized with ease. Especially, in case of stereoscopic 3D TV images, it is more important for the viewer to watch TV within an optimal viewing range.
For a 3D TV receiver using polarized glasses, in addition to the distance between the viewer and the screen important, also the vertical viewing angle are important factors. For instance, in case of a 2D LCD TV, a vertical viewing angle is about 160° or more. On the other hand, in case of a polarized glassed type 3D LCD TV, a vertical viewing angle is merely about 10° due to use of a retardation film for generating polarized light with respect to the right and left images. If the viewer watches TV outside of the viewing angle, an image may be erroneously recognized as a white blurred image having a very low gamma value, or as a black image having a very high gamma value.
Therefore, in order for the viewer to more properly watch 3D images provided from a 3D TV receiver with optimal contrast and brightness with minimal fatigue, the viewer has to be within the optimal viewing range and also within the optimal viewing angle. However, it is not easy for the viewer to check his or her current position and to adjust his position while viewing television. Furthermore, while selecting a proper position, the viewer may not concentrate on the program being shown, or may such position re-alignment can cause inconvenience. For example, the elderly or children may experience difficulties in deciding and moving into the proper viewing position.